The 10-Percent Rule

This safe, easy-to-follow method will help you increase your mileage in a sound manner.

The 10-percent rule (10PR) is one of the most important and time-proven principles in running. It states that you should never increase your weekly mileage by more than 10 percent over the previous week.

The 10PR gains its importance from the fact that the vast majority of running injuries are overuse injuries. They occur when you run too much or increase your weekly training program too quickly. Say you've been running 15 miles a week. For some reason–perhaps you want to prepare for an upcoming race or you just feel that you're ready–you decide to pick up your training. Instead of running 5 miles three times a week, you manage to fit in five 5-milers. Your training increases from 15 miles a week to 25 miles a week–a 67 percent increase.

The week of the race, your knee starts throbbing. By Saturday, you're hobbling. You can't ignore the handwriting on the wall. You're not going to be able to run the Sunday morning race. You have a knee injury.

For runners, the biggest enemy is often their own energy and enthusiasm. You're feeling great, so you figure that you can handle more training. A friend has challenged you to enter a race. Everyone in your department at work has decided to get in shape for an upcoming charity run. Or maybe you've been bitten by the marathon bug.

Events like these are big motivators, so you plunge excitedly into the training. Great–except for one thing. Your body doesn't share in your enthusiasm. It follows one simple, unchanging principle: gradual adaptation to stress.

The gradual adaptation principle is one of the many examples of the body's genius. Without it, no one could ever climb Mount Everest, swim the English Channel, or run a marathon. With it there are almost no limits to what you can achieve. But you can't bend the rules, or the system breaks, and you get an injury or pick up a cold or suddenly become fatigued.

Follow the 10PR, on the other hand, and your body gets stronger and fitter. If you're running 10 miles a week now, and you want to increase your training, run 11 miles next week. And 12 the week after that. And 13 the week after that. This may look like agonizingly slow progress, but in just 8 to 10 weeks, you could be running 20 miles a week.

Continue on the same path, and you'll be running 40 miles a week just four months after you started building up from 10. And 40 miles a week, believe me, is a lot of running. It can take you anywhere you want to go.

Once again, the race goes to the tortoise. In running, you will almost always win if you follow the path of slow-but-sure.